There is very little that can get you in in and of itself. However, 6-8 as a freshman is very good, may get you to the USAMO this year, and may lead you to further honors, perhaps even MOSP if you do well on the USAMO in the next couple years. MOSP participants are more or less guaranteed to get in to MIT, but short of that, there's no such thing as "enough for entrance."

"Lowest scores"? I'm sure there are plenty of people at MIT who haven't taken the AIME at all. It's not some sort of required thing. No paranoia, please.

A 6 to 8 puts you in the top 50-100 freshmen. Please put yourself in perspective, this is already a huge achievement, and MIT couldn't possibly create a class of only the top AIME scorers.

Then again, this year's AIME seemed, at least to me, relatively easy. Who knows what a 6 is now?

In any case, since you're still a freshman, anything can change. I tell you this as someone who got a 1 freshman year, an 8 sophomore year, and yesterday, a 10.